Metal plated carbon material and method of producing thereof

ABSTRACT

A metal plated carbon material containing at least one metal chloride compound disposed between graphite layers to form a graphite intercalation compound, and a metal plated layer being formed on a front surface of the metal plated carbon material. A method of producing the metal plated carbon material comprising the steps of immersing a graphite intercalation compound in an electroless plating solution for 6 to 30 hours, and forming a metal plated layer on a surface of the graphite intercalation compound with an excellent adherence thereto.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a carbon material having a metal platedlayer suitable for an electro-conductive element and a heat-conductiveelement and to a fabrication method thereof.

2. Description of the Prior Art

In recent years, in many industrial fields such as in home electricindustries, automobile industries and aerospace industries, it has beenrequested to provide miniaturized, highly integrated and personalizedproducts. Thus, electromagnetic shielding materials, light-weightelectro-conductive materials, large heat-conductive materials and thelike that fulfill the requirements have been developed.

Various metal materials have been used for such materials in question.However, these materials tend to be heavy.

On the other hand, since carbon materials have excellent dynamiccharacteristics, such as having light weight, large tensile strength,and large modulus of elasticity, as well as high electro-conductivityand large heat-conductivity, these materials have been used forstructural members especially in the fields of sports industries,leisure industries, and aerospace industries. However, there have beenvery few applications of carbon materials based on the characteristicsof their electro-conductivity and heat-conductivity, and only carbontype electro-conductive paints and bonding agents could have been foundin low power electric circuits.

This is because the electro-conductivity of the carbon materials is muchlower than that of metal conductors. For example, as a means forimproving electro-conductivity of carbon fibers, a technology formetal-plating the surface of carbon fibers has been proposed as seen inJapanese Patent Laid-Open Publication No. 2-189811. However, in atreatment of electrolytic-plating, since the electro-conductivity of thecarbon fibers is not high, a speed of film forming is slow and,moreover, a uniform film could not be formed. On the other hand, in atreatment of electroless plating, since the activation process iscomplicated and also a speed of film forming is slow, accordingly, theproductivity has been poor.

Another type technology such as for milling or chopping continued carbonfibers of polyacrylonitrile (PAN) type or pitch type has been proposedfor providing carbon fibers shortened in length. Yet further, anothertechnology has been proposed wherein vapor-phase grown carbon fibers(VGCF) obtained through thermal decomposition of a raw organic compoundby the act of catalysis of ultra fine particles of fibrous metal ormetal-organic compounds, and compounding discrete carbon fibers of thusobtained VGCF with a plastic material so as to use the resultantmaterial as a carbon fiber reinforced plastic or an electro-conductiveplastic.

However, the electro-conductivity of such composite materials has anelectric resistivity of 10⁻² Ω cm at the most or as a limit. A metalplating treatment for such discrete carbon fibers is disclosed in, forexample, Japanese Patent Publication No. 62-15637, wherein a method ofpretreatment is described for forming a thin film of a noble metal onthe discrete carbon fibers for electroplating. However, this method hasa problem such that a uniform layer can hardly be formed on fine fibers.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to eliminate theproblems encountered in the prior art method and to provide a carbonmaterial with a metal plated surface layer having characteristics ofexcellent uniformity and excellent adherence and a method of producingthe same.

An aspect of the present invention is to provide a metal plated carbonmaterial containing at least one metal chloride disposed betweengraphite layers, and being formed a metal plated layer on a surfacethereof.

Another aspect of the present invention is to provide a method ofproducing a metal plated carbon material, wherein immersing a graphiteintercalation compound, which is synthesized by a carbon material and atleast one metal chloride, in an electroless plating solution, and thenforming a metal plated layer on a surface of the graphite intercalationcompound.

The metal plating carbon material according to the present invention hasa uniformly metal-plated layer, thus provided are high adherence of themetal plated layer and high electro-conductivity.

In addition, according to the method of the present invention, a metalcan be uniformly plated on a carbon material, in particular, on a powdercarbon material. The metal plating on fine carbon fibers has beendifficult by conventional technologies, however, in accordance with thisinvention, such difficulty can be eliminated and a metal layer can beplated even on fine carbon fibers. The adherence of the metal platedlayer onto the carbon material and the electro-conductivity of theresultant material are very high.

These and other objects, features and advantages of the presentinvention will become more apparent in light of the following detaileddescription of embodiments of the present invention, as illustrated inthe accompanying drawings.

DESCRIPTION OF PREFERRED EMBODIMENTS

A carbon material used in the present invention is natural graphitepowder, artificial graphite powder, kish graphite powder, carbon fibers,graphite fibers, or the like.

The natural graphite, artificial graphite and kish graphite arepreferable to powder by milling to an order of 100 mesh or less. Sincethe graphite has a two-dimensional structure, it is difficult to form auniform metal plated layer when large crystal is employed. The carbonfibers or graphite fibers used in one embodiment of the presentinvention are continuous carbon fibers or continuous graphite fibersprovided by spinning a melted macro-molecule precursor, performingnon-melting heat treatment in an oxidizing atmosphere, performingcarbonizing heat treatment in an inert gas atmosphere at a temperatureof 1000° C. or more, and then performing high temperature heat treatmentin an inert gas atmosphere at a temperature of 1500° C. or more,preferably 2500° to 3500° C. The carbon fibers or graphite fibers usedin another embodiment of the present invention are discontinuous carbonfibers or discontinuous graphite fibers provided by chopping or millingthe continuous carbon fibers or continuous graphite fibers into anydesired length.

The macro-molecule precursor used in still another embodiment of thepresent invention is a synthetic resin, for example, polyacrylonitrile,rayon, polyvinyl alcohol, vinyl chloride, phenol, aramid, polyamide orpolyimide, or a natural macro-molecular compound such as of a pitch ofoil or coal.

Further, vapor-phase grown carbon fibers (VGCF) are also used in thepresent invention. The vapor phase grown carbon fibers (VGCF) are carbonfibers having a length of 1000 μm or less and a diameter of 1 μm orless. These vapor-phase grown carbon fibers are produced by gasifying acarbon supplying substance and contacting it with a catalyst of ultrafine metal particles or a metal organic compound, or a catalyst of ultrafine metal particles of a transition metal, such as iron, nickel orcobalt, whereas when the catalyst is of metal particles, a diameter ofparticles should be 300 μm or less, when the catalyst is of a metalorganic compound, it should be the one usable as a state of liquid orsolution, or especially the one vaporizable such as metallocene. Thecontact of the gasified carbon supply substance with said catalyst isimplemented in a reacting region ranging from 900° to 1500° C. alongwith a carrier gas such as of hydrogen, carbon monoxide, carbon dioxideor the like. The carbon supplying substances are, for example, analiphatic hydrocarbon group such as methane, ethane, propane, propyleneand the like, an aromatic hydrocarbon group such as benzene, toluene andthe like, an alicyclic hydrocarbon group such as cyclohexane,cyclooctane and the like, an alcohol group such as ethanol, butanol,octanol and the like, a ketone group such as ethyl isobutylketone,cyclohexane and the like, a nitrified organic compound such ashexylamine and the like, a sulfurated organic compound such asoctylmercaptane and the like, and a chlorinated compound such as carbontetrachloride and the like.

The vapor-phase grown carbon fibers (VGCF) obtained in such a process asdescribed above are treated by heat in an inert gas atmosphere such asargon at a temperature of 1500° to 3500° C., preferably 2500° to 3500°C., for 3 to 120 minutes, preferably 30 to 120 minutes. As a result,graphite fibers having highly developed graphite structure are obtained.

In accordance with this invention, the above-mentioned carbon materialand at least one of metal chlorides are synthesized to form a graphiteintercalation compound.

The metal chlorides to be used in the present invention are, forexample, magnesium chloride, stannous chloride, palladium chloride, ironchloride, aluminum chloride and nickel chloride.

The metal chloride graphite intercalation compound is provided by anysynthesizing method such as mixing method, two-bulb method, solventmethod, melt salt method, electro-chemical method or the like. Next, anexample of the synthesizing method of the graphite intercalationcompound corresponding to the mixing method above will be described.

The carbon material and the metal chloride compound are uniformly mixedand placed in a reacting vessel. The inner pressure of the reactingvessel is reduced in pressure to an order of 10⁻⁶ Torr. Then, thereacting vessel is closed airtightly. At this point, a reactionaccelerator such as chlorine gas having a pressure of several Torr maybe charged in the reacting vessel. The closed vessel is heated up to aproper temperature of 300° to 700° C. The reaction is continued forseveral minutes to several days, preferably one hour to three days,after setting the appropriate temperature. As a result, a metal chloridegraphite intercalation compound containing the metal chloride betweengraphite layers is obtained.

The metal plating treatment is performed by immersing theabove-mentioned metal chloride graphite intercalation compound into anelectroless plating solution containing film forming metal ions. A timerequired for finishing the metal plating treatment depends on thethickness of the film to be formed, however, a proper plating can beobtained in 2 to 40 hours, preferably 6 to 30 hours. Even if the metalplating is carried out for more than 40 hours, the thickness of themetal layer will not increase. If the time of metal plating is less than2 hours, it is impossible to obtain a uniform metal plated layer.

It is possible to add some additives such as a brightener, anantioxidant, and the like to the electroless plating solution besidesthe film forming metal ions.

Examples of the present invention and comparisons will be describedhereinafter.

EXAMPLE 1

PAN type carbon fibers (TOREKA MLD300, made by TORAY K. K.) on themarket were heated in an argon gas atmosphere at 3000° C. so as toproduce graphitized fibers. The resultant graphite fibers of 5 gramswere mixed with palladium chloride anhydride of 5 grams. The mixture wasthen placed in a reacting vessel and heated up to 120° C. The reactingvessel was reduced in pressure to 10⁻⁶ Torr or less and maintained for20 hours or more. Thereafter, chlorine gas was charged into the reactingvessel until the pressure reaches to 0.1 Torr and then the reactingvessel was closed airtightly. The reaction was continued for 3 days at420° C. As a result, obtained was a palladium chloride graphiteintercalation compound containing palladium chloride disposed betweengraphite layers.

In the next step, the palladium chloride graphite intercalation compoundwas immersed in an electroless plating solution and stirred at a roomtemperature for 20 hours so as to perform copper plating treatment. As aresult, a metal plated carbon material A was obtained.

EXAMPLE 2

Pitch type carbon fibers (GURANOC XN40, made by Nippon Oil K. K.) on themarket were treated in the same way as in the Example 1 to synthesize apalladium chloride intercalation compound. Thereafter, the palladiumchloride intercalation compound was immersed in an electroless platingsolution and stirred at a room temperature for 20 hours so as to performcopper plating treatment. As a result, a metal plated carbon material Bwas obtained.

EXAMPLE 3

Benzene was utilized as a carbon supplying substance for providingcarbon fibers. Ferrocene was employed as a catalyst. Hydrogen was usedfor a carrier gas. Vapor phase grown carbon fibers (VGCF) having alength of 50 μm or less and a diameter of 0.01 to 0.5 μm were heated inan argon gas atmosphere at 3000° C. As a result, graphite vapor phasegrown carbon fibers were obtained. Thus obtained graphitized vapor phasegrown carbon fibers were treated in the same process as in the Example 1so as to synthesize a palladium chloride intercalation compound. Thepalladium chloride intercalation compound was immersed in an electrolessplating solution and stirred at a room temperature for 20 hours so as toperform copper plating treatment. As a result, a metal plated carbonmaterial C was obtained.

COMPARISON 1

The PAN type carbon fibers (TOREKA MLD300, made by Toray K. K.), whichwere the same as those used in the Example 1, were directly immersed ina copper sulfate plating solution and stirred at a room temperature for20 hours so as to perform copper plating treatment. As a result, a metalplated copper material X was obtained.

COMPARISON 2

By using the pitch type carbon fibers (GURANOKKU XN40, made by NipponOil K. K.), which were the same as those used in the Example 2, and inthe same steps as in the Comparison 1, the copper plating treatment wasperformed. As a result, a metal plated carbon material Y was obtained.

COMPARISON 3

In the same way as in the Example 3, benzene was used for a carbonsupplying substance for carbon fibers. Ferrocene was employed as acatalyst. Hydrogen was used for a carrier gas. Vapor-phase grown carbonfibers (VGCF) having a length of 50 μm or less and a diameter of 0.01 to0.5 μm grown at 1100° C. were treated by heat in an argon gas atmosphereat 3000° C. Thus obtained graphitized vapor-phase grown carbon fiberswere treated in the same copper plating treatment as in theComparison 1. As a result, a metal plated carbon material Z wasobtained. In the above Examples, the obtained metal plated carbonmaterials A, B, and C had metal plated layer adhered tightly torespective carbon material. Among these, the adherence of the metalplated carbon material C was excellent.

On the other hand, in the above comparisons, the adherence of the metalplated layers of the metal plated carbon materials X, Y, and Z was poorand they could hardly be afforded for practical use.

Although the present invention has been described with respect to thepreferred embodiments thereof, it should be understood by those ofordinary skilled in the art that various modifications can be madewithout departing from the scope of this invention. Accordingly, thisinvention is not to be limited except as by the appended claims.

What is claimed is:
 1. A metal plated carbon material, comprising acarbon material of an intercalation compound including at least twographite layers and at least one metal chloride compound between thegraphite layers, and a uniform layer of metal plated on the surface ofsaid carbon material.
 2. The metal plated carbon material as claimed inclaim 1, wherein said graphite layers are made from polyacrylonitrilecarbon fibers.
 3. The metal plated carbon material as claimed in claim1, wherein said graphite layers are made from pitch carbon fibers. 4.The metal plated carbon material as claimed in claim 1, wherein saidgraphite layers are made from vapor-phase grown carbon fibers.
 5. Themetal plated carbon material as claimed in claim 1, wherein saidgraphite layers are made of natural graphite.
 6. The metal plated carbonmaterial as claimed in claim 5, wherein said natural graphite is crushedinto a powder having a size of 100 mesh or less.